1. Field of the Invention
The present invention relates to a chip-type piezoelectric component having a lamination structure including a piezoelectric element, a sealing substrate, and external electrodes on side surfaces of the laminated structure.
2. Description of the Related Art
A chip-type piezoelectric component including a laminated structure of sealing substrates and a piezoelectric element has been known in the art. For example, Japanese Unexamined Patent Application Publication No. 10-200368 discloses a chip-type piezoelectric component including a piezoelectric element on both principal surfaces on which mutually opposed vibration electrodes and terminal electrodes connected to the vibration electrodes are provided, an adhesive layer provided on the principal surface at least excluding the vibration electrode area of the piezoelectric element, and a laminated body including seal substrates bonded via the adhesive layer, wherein external electrodes for pulling the terminal electrodes out on the side surfaces at the end of the laminated body are provided. A recess in which the adhesive layer is not present is provided on the principal surface on which the terminal electrodes at the outermost sides of the piezoelectric element are provided, the external electrodes being arranged so that the side surfaces at the end of the laminated body, the side surfaces of the terminal electrodes, and the recess are electrically connected to one another.
Practical methods for forming the external electrodes that have been disclosed include a wet deposition method such as plating, a dry deposition method such as sputtering, a method for depositing a first layer by the dry deposition method such as sputtering, followed by forming a second layer by electroplating, and a method for forming the external electrodes on the side surfaces at the ends of the laminated body including conductive layers formed by the wet deposition method or by the dry deposition method, after forming the conductive layers by embedding a conductive paste in the recess.
However, since the conductive film deposited on the external electrode by wet deposition or dry deposition is relatively thin, the conductive film is attacked by a complexing agent in the plating bath rendering the film strength low, and this yields insufficient reliability in bonding between the film and the laminated body.
When the external electrodes are provided on the side surfaces at the ends of the laminated body after forming a conductive portion in the recess, on the other hand, the external electrodes are deposited in two steps, also yielding low bond strength due to poor workability in addition to the external electrodes being formed as thin films.
To overcome the above-described problems, preferred embodiments of the present invention provide a chip-type piezoelectric component including external electrodes that are easily formed while greatly increasing bond strength of the external electrodes.
Preferred embodiments of the present invention provide a chip-type piezoelectric component including a piezoelectric element on both principal surfaces of which mutually opposed vibration electrodes and terminal electrodes connected to the vibration electrodes are provided, an adhesive layer provided on the principal surface of the piezoelectric element at least excluding the vibration electrode area, and a laminated body including a seal substrate bonded via the adhesive layer, external electrodes being arranged for pulling the terminal electrodes out on the side surfaces at the ends of the laminated body, wherein the adhesive layer is not provided on the principal surface at the outermost side of the piezoelectric element, but a recess exposing the terminal electrode is provided on the side surface at the end of the laminated body, the external electrode extends continuously along the direction of thickness on the side surface at the end of the laminated body, and is defined by a monolithic conductive film embedded in the recess, and the conductive film is formed by coating and baking a conductive paste including a resin composition and metal particles.
Electrical continuity between the terminal electrodes of the piezoelectric element and the external electrodes is ensured in preferred embodiments of the present invention, because the external electrodes defined by a monolithic conductive film embedded in the recess extend continuously along the direction of thickness on the side surfaces at the end of the laminated body. In addition, the external electrodes are easily formed because they are not formed in two steps. Bonding strength between the laminated body and the external electrode is greatly improved by a wedge effect due to the conductive paste penetrated in the recess since the external electrode including the conductive paste is continuously formed on the side surface at the end of the laminated body and in the recess. Consequently, the electrode is prevented from being peeled by the attack of the complexing agent in the plating bath when the plating film is formed on the surface of the external electrode.
Preferably, a metal plating layer having a good soldering wettability is provided on the outermost layer of the external electrode. Good wettability of the solder cannot be obtained by direct soldering of the external electrode on which the conductive paste has been baked. However, a chip-type piezoelectric component with a good compatibility with soldering is obtained by providing a metal plating layer on the outermost layer of the external electrode.
Preferably, the viscosity of the conductive paste before coating is about 50 Paxc2x7s or less, in order to allow the conductive paste to easily penetrate into the recess by capillary action, thereby preventing occurrence of insufficient filling of the conductive paste.
Preferably, the conductive paste includes at least about 80% by weight of the metal particles in order to improve conductivity as well as adhesive property to the plating layer to be provided thereon.
Preferably, the conductive paste is transferred on the side surface at the end of the laminated body by allowing the conductive paste before hardening to rise from discharge holes having slit grooves or a belt with a number of perforated holes, followed by pressing the conductive paste onto the side surface at the end of the laminated body so that the side surface crosses the discharge holes, in order to allow the conductive paste to easily penetrate into the recess without significant formation of cavities. Consequently, electrical continuity between the terminal electrode and external electrode as well as bonding of the external electrode are substantially improved.
When the conductive paste is coated on the laminated body by immersing the entire end surface of the laminated body into a dip layer of the conductive paste, as is used conventionally, air is trapped in the coating layer thereby preventing the conductive paste from penetrating to the bottom of the recess. Consequently, the conductive paste should be filled in the recess of each piezoelectric component using a dispenser. However, the coating work is difficult and insufficient in reliability because the recess has a finite size. In the case of the transfer method taking advantage of the discharge holes including a slit groove and a belt with perforation holes, on the other hand, workability is superior, and in addition, the conductive paste is securely filled in the recess because air cavities are not significantly formed by the process of pressing the conductive paste onto the surface at the end of the laminated body after allowing the conductive paste to rise from the holes.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the attached drawings.